<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>

		<input type="text">
		<select>
			<option>+</option>
			<option>-</option>
			<option>*</option>
			<option>/</option>
		</select>
		<input type="text">
		<button>=</button>
		<input type="text" />
		<script>
			练习: 实现加减乘除的计算器
		</script>
	</body>
</html>
